Railway signal system



Nov. 7, 1933.

E. L. LORD 1,934,366

RAILWAY SIGNAL SYSTEM Filed Dec. 29, 1932 I l L: :.1

l T, :L 2

WWA/55.9:

Patented Nov. 7, 1933 RAILWAY SIGNAL SYSTEM y Edward L. Lord, ,Glensida Pa., assigner to The Electric Storage Battery ration ci New Jersey Company, a corpo- Application December 29, 1932 Serial No. 649,247

3 Claims. l (Cl. 24S- 41) The invention relates to railway signal systems and especially to systems in which a track circuit is provided into which a battery anda relay are connected in series, the relay having contacts for controlling a signal circuit in the usual manner whereby the circuit is opened when the coil of the relay is shunted by the wheels andaxles of. a car or train in the track section.

An object of the invention is to increase the speed and reliability of the relay operation under Varying conditions of the track circuit'and especially in the case of a train shunt of comparatively high resistance such as that of a light weight car.

In carrying out my invention I provide in series with the relay coils a resistor of special characteristics whose resistance increases withV a decrease of current therethrough. A

`My invention will be more clearly understood by reference to the single iigure of the accompanying drawing in which is shown diagrammatically a signal system embodying the invention.

In the drawing,

1, 2 are the opposite rails of a track section, insulated from the adjacent track sections by insulating joints 3, 4, 5 and 6. At one end of the track section is the battery '7, connected across the opposite rails in the usual manner, with the adjustable limiting resistance 88 in series there- "0 with. At the other end of the track section is the relay 8, whose coils 9 and l0 are connected in series across the opposite rails 1, 2. The relay contacts 16, 17 are connected in series with the relay circuit 12, 13 supplied with current by the 'battery 1l, and connected to the operating coil 14 of the signal 15. The apparatus and'circuits thus far described may be of any of the well known designs usually employed for the purpose. At 18 is shown a vehicle running on the rails and adapted, upon entering the track section l, 2, to shunt the relay coils 9, 10, causing the relay Contact member 19 to drop, opening the signal circuit and causing the signal to drop to the danger position.

In series with the relay coils 9, and preferably connected between said coils is shown a special resistor R having such a characteristic that its resistance increases with decrease of current therethrough. While Various forms of resistors having such a characteristic are known, I have found that a unit consisting of one or more copper oxide coated copper disks such as have been developed for use in a rectiiier 0i the dry contact type give excellent results. Other ex- 'amples of materials which show a negative current resistance characteristic-are many of the metallic oxides and sulphides. In most cases, these characteristics depend upon the changeof temperature caused by change of current, which introducessome time delay in attaining the desired result. However, in some applications this time delay would not be objectionable and the denition of a negative current-resistance characteristic is intended to cover all suchmaterials, whether or not the change of resistance is accompanied by a change of temperature. In the copper-copper oxide disks mentioned in the preierred embodiment of this invention, the change inresistance is practically coincident with the change of current and'is not dependent upon any appreciable change of temperature although a minute change of temperature may possibly occur at the points of contact between the metal and theoxide. These should be connected in the direction to permit the current to now, and in order to provide a suitable resistance Value and suitable variation of resistance with changes of current, several such disks may be connected in series and several of these series groups may be connected inparallel. As an example, I find that with a standard 4 ohm tract relay, four coppercopper oxide disks connected in parallel give excellent results.

The operation of this arrangement'is explained as follows: Assume the limiting resistance 88 to be so adjusted that with no train shunt in the track section the current through the relay coils 9, 10 is 0.125 ampere, suiicient to hold the relay contacts closed. Now let the train shunt 18 enter the track section, diverting current from the relay coils. This train shunt may have so high a resistance value that, in the case of the usual track circuit with xed resistance values, the reduction of current in the relay coils will not be suiiicient to cause the contact arm 19 to drop. With the arrangement of my invention, a reduction in the current passing through the relay coils 9, 10 and the resistor R. will cause an increase in the value of the resistor on account of the special characteristic of the element R and this increase in resistance will cause a greater reduction of current than would occur if the resistance values Y time than is required with the usual arrangement of apparatus, and this time factor is an important feature and of very marked utility in cases where the track section is very short and a single car may pass over it at Very high speed.

My arrangement also affords better protection than the standard apparatus in the case of a broken rail where the leakage through the ground around the break may be sufficient to hold the relay in the contact making position and thus fail to give a danger signal. With my device the reduction in current due to the break in the rail causes the resistance of the element R to increase and produce a further reduction of current suilicient to allow the relay to open under conditions where this would not` otherwise occur.

In the diagram the resistor R is shown connected between the two coils 9 and 10 of the relay. Under ordinary operating conditions it will make no difference whether this resistor is connected as shown or is connected between the relay coils and either side of the track. However, in the case of a lightning stroke, the resistor R if connected outside of the relay might be damaged and short circuited without affecting the relay itself. In such case the current in the relay coils would be abnormally increased and the train shunt might fail to reduce the current in the coils to a suiiicient extent to open the relay. With the resistor connected between the coils, as shown, a stroke of lightning which would short circuit the resistor would also undoubtedly burn out the coils and open the circuit or the relay causing the signal to drop to the danger position.v

While, as mentioned above, there are a number of materials which would be used for the resistor R, having a characteristic .producing an increase of resistance with` a reduction in the amount of current flowing through them, the

copper-copper oxide disks, which I prefer to use, have a distinct advantage in that this characteristic is developed instantly upon change of current. Other materials which depend upon change of temperature to produce this effect require a longer time to act and are therefore not as effecftive to secure quick results. In the appended claims I refer to a resistor having a negative current-resistance characteristic, which is to be dened as a characteristic in which the resistance value increases with decrease in the current and vice versa. l

I claim:

1. In a railway signal system having a relay provided with two coils, a track circuit comprising in series connection a source of current, a portion o f the track, the relay coils having direct connections with said track, and a resistor having a negative current-resistance characteristic'connected between said coils.

2. In a railway signal system the combination of a track section, a source of current connected thereto, a relay having two operating coils directly connected to the opposite rails of the track section, and, in series therewith and between said coils, a resistor having a negative' currentresistance characteristic, said' resistor comprising a metallic disk whose current carrying contactl surface is coated with a compound of the metal with a non-metallic element.

3. In a railway signal system the combination oa track section, a source of current connected thereto, a relay having two operating coils directly connected to the opposite rails ofthe track section, and, in series therewith and between said coils, a resistor having a negative current-resistance characteristic, saidl resistor comprising a copper disk whose current carrying contact surface is coated with copper oxide. l

EDWARD L. LORD. 

